Conventionally, in general, a CD, a DVD, or a Blu-ray (registered trademark) Disc is widely known as an optical disc. In recent years, a further improvement in the recording density of the optical disc is desired. In order to realize an optical disc information device that records or reproduces information at a high density, it is necessary to reduce a track pitch of the optical disc or improve the density of the optical disc in a line direction.
In order to improve the recording density of the optical disc information device, it is effective to reduce the track pitch of the optical disc.
However, when the track pitch is reduced, a problem arises that crosstalk in which a signal recorded on an adjacent track adjacent to a scanned track scanned with a converged light flux leaks into a reproduction signal is increased, and the signal having leaked thereinto becomes a noise of the reproduction signal.
To cope with this, in a conventional optical disc information device for solving the above problem, for example, as described in Patent Literature 1, a photodetector that is split into three portions in a direction orthogonal to a track is used in a one-beam optical system, and the crosstalk of an output signal S is cancelled by performing an arithmetic operation on light amount signals C, R, and L detected in central, right, and left light receiving sections based on Expression shown below.S=K*C+R+L                 K: constant        
In addition, Patent Literature 2 discloses a configuration in which only a signal from a central light receiving section is subjected to waveform equalization using a transversal filter. In this example, an output signal from the central main light receiving section is subjected to waveform equalization so as not to be correlated with output signals from left and right sub-light receiving sections.
FIG. 27 is a view showing the configuration of a conventional photodetector. Light receiving sections 901a, 901b, and 901c obtained by splitting the photodetector into three regions receive a light beam 900, and output output signals corresponding to the amounts of the light emitted to the light receiving sections 901a, 901b, and 901c to amplifiers 902a, 902b, and 902c. The amplifiers 902a, 902b, and 902c amplify the output signals from the light receiving sections 901a, 901b, and 901c. Output signals from the amplifiers 902a, 902b, and 902c are converted from analog signals to digital signals by A/D converters 903a, 903b, and 903c. 
Output signals of the A/D converters 903a and 903c to which the output signals of the light receiving sections 901a and 901c corresponding to side edge portions of the light beam 900 are given are directly inputted to an adder 905. An output signal of the A/D converter 903b to which the output signal of the light receiving section 901b corresponding to a central portion of the light beam 900 is given is inputted to the adder 905 via a transversal filter 904. The adder 905 adds up the input signals and outputs a signal obtained by the addition to an amplifier 906. An output signal of the amplifier 906 is used as an information reproduction signal.
The output signal of the adder 905 is given to a factor control circuit 907 for feedback control, and an output signal of the factor control circuit 907 is given to the transversal filter 904. The factor control circuit 907 controls an integrating factor of the transversal filter 904. With this, the transversal filter 904 performs the waveform equalization on the output signal of the light receiving section 901b corresponding to the central portion of the light beam 900 such that the output signal thereof is not correlated with the respective output signals of the light receiving sections 901a and 901c corresponding to the side edge portions of the light beam 900, i.e., such that the respective output signals of the light receiving sections 901a and 901c corresponding to the side edge portions of the light beam 900 do not interfere with the output signal thereof.
The technology described in Patent Literature 1 has an effect of reducing the crosstalk as the signal leaked from the adjacent track by a specific amount. However, when the track pitch is reduced and the crosstalk is increased, there are cases where the effect of the technology described in Patent Literature 1 alone is not sufficient.
The technology described in Patent Literature 2 has the configuration in which the output signal of the light receiving section corresponding to the central portion is subjected to the waveform equalization so as not to be correlated with the output signals of the light receiving sections corresponding to the side edge portions. However, the output signal of the light receiving section corresponding to the central potion and each of the output signals of the light receiving sections corresponding to the side edge portions include a signal component of a main track and a crosstalk signal component from an adjacent track at different ratios. Accordingly, a condition of a waveform equalizer for minimizing the crosstalk signal component from the adjacent track is different from a condition of the waveform equalizer for eliminating the correlation between the output signal of the light receiving section corresponding to the central portion and the output signals of the light receiving portions corresponding to the side edge portions. Consequently, even when the output signal of the light receiving section corresponding to the central portion is subjected to the waveform equalization using the waveform equalizer that eliminates the correlation between the output signal of the light receiving section corresponding to the central portion and the output signals of the light receiving sections corresponding to the side edge portions, there still remains a problem that the crosstalk amount is not minimized.